Method of thermal cracking of hydrocarbons

ABSTRACT

Thermal cracking apparatus in which the reaction transfer, quenching and separation are carried out in circulating molten metals which are maintained molten by circulation through a preheater tube prior to circulation through the reaction tube. The preheater tube and the reaction tube are heated by burners. Feed stock or a diluent such as steam is sprayed into the quenching tower through the reaction tube to assist the circulation.

United States Patent 151 3,696,166 Ozawa et al. 1451 Oct. 3, 1972 [54]METHOD OF THERMAL CRACKING [56] References Cited 0F HYDROCARBONS UNITEDSTATES PATENTS [72] Inventors: Tokuji Ozawa, 78, Minaminagao- 2 112 1493/1938 Ed d 196 18 war s mach" saka" uyeda' 2,931,843 4/1960 Bruns..260/683 M 2,543,743 2/1951 Evans ..260/679 gasaki; Ryosuke Hashimoto,1413, 2,197,257 4/1940 Burk ..260/680 NobidomeNilzamachi,l(itaadachigun, Saitama; Shigenorl Suzuki, 6, 'f 'f' GamzShibatanimachi 2 chom S Assistant Examiner-J. M. Nelson umlryaAttorney-Howson and Howson shlku, Osaka, all of Japan 22 Filed: June 15,1970 7] ABSTRACT 21 L 45,959 Thermal cracking apparatus in which thereaction 0 transfer, quenching and separation are carried out in gqgphegg pl'lol'lty Data circulating molten metals which are maintainedmol- June 21, 1969 Japan ..44/49,604 ten by circula ion through apreheater tube prior to circulation through the reaction tube. Thepreheater 52 vs. C] ..260/683 R, 208/125, 208/48, tube and the reactiontube are heated y burners- 23/2094 2 0 79 23 2 Feed stock or a diluentsuch as steam is sprayed into 51 Int. Cl ..C07c 3 00 the quenching towerthrough the reaction tube to [58] Field of Search ....'....208/48, 122;260/679, 683; assist the eireulatien- 6 Claims, 1 Drawing Figure METHODor THERMAL CRACKING or HYDROCARBONS The present invention relates to amethod of producing olefms such as ethylene by thermal cracking ofhydrocarbons in the presence of molten metals as circulating fluid.

For production of unsaturated hydrocarbons by thermal cracking ofhydrocarbons, there have been publicly known tubular cracking furnace ofexternal heating system, heat carrier recycle process and partialcombustion process. However, in the known apparatuses, it is almostimpossible to use hydrocarbons extending over a wide range from napthafractions of low boiling points to crude oil in which are includedkerosene, light oil, heavy oil and crude oil. If such hydrocarbons areused, long run continuous operation is interrupted by cracked cokedeposited and accumulated in reactor, transfer line or on the surface ofquencher tubes. Further, conventional apparatuses have not sufficientfunctions in all of points of the reaction system, quenching system,heat recovery system and system of cracked coke removal. For fulfilfunctions of those systems, a considerably complicated apparatus havebeen required and not practical.

The present invention is to provide very simple thermal cracking methodand apparatus in which hydrocarbons extending over a wide range fromoils of lighter fraction to oils of heavier fraction such as heavy oiland crude oil can be used, which is fit for long run continuousoperation and which is provided with all of thermal cracking, quenching,heat recovery and cracked coke removal systems.

The apparatus according to ,the present invention is characterized bybeing composed of a tubular cracking furnace containing a preheater tubefor preheating molten metals and a reaction tube for thermal cracking ofhydrocarbons and a quenching tower for quenching reaction products andmolten metals and also for separating and removing cracked coke, themolten metals being circulated in the apparatus, whereby hydrocarbonsare thermally cracked effectively and long run continuous operation canbe effected.

In a thermal cracking apparatus for hydrocarbons, a trouble is caused byaccumulation of cracked coke, etc., in the reactor, transfer line andquencher. Under a certain cracking condition, the coke, etc., are due tothe amount of Conradson carbon in the crude oil in general. In heavierhydrocarbons containing a larger amount of Conradson carbon, by-producedcoke, etc., are larger and cannot decreased into zero, even if they canbe reduced to some extent by selection of operation condition. Theapparatus of the present invention is not provided with reactor,transfer line and quencher sections which invite accumulation of crackedcoke. In the apparatus of the present invention, the reaction, transfer,quenching and separation of cracked coke, etc., are carried out inmolten metals as circulating fluid. Accordingly, troubles caused bycrackedcoke as in the conventional apparatuses are not observed in theapparatus of the present invention.

The construction and effects of the present invention will be describedwith reference to the drawing which is an explanatory illustrationshowing the method of the present invention.

Naptha, kerosene, light oil, heavy oil, residual oil or crude oil eachas petroleum fraction in liquid or in vapor form, preferably pre-heated,is supplied alone or together with a diluent such as steam under a highpressure into a vertically or horizontally arranged reaction tube 3 in acracking furnace 5 through suitably arranged feed stock supplyingnozzles 1. By the feed stock injection, molten metal heated to atemperature of 700-1,000 C in a pre-heater 4 is sucked into the reactiontube. While passing through the reaction tube 3, the hydrocarbons arecontacted effectively with the molten metal and thermally cracked. Heatenergy required for the cracking is given by burners 2 through an outerwall of the preheater tube 4 or reaction tube 3. A long run continuousoperation is possible, because cracked coke produced in the reactiondoes not deposit on the wall of the reactor 3 but in the circulatingmolten metal. Flue gas is discharged through 6. The reaction tube 3 isinserted and opened in a quenching tower 7 in which a quencher tube 8 isset. The molten metal of 700l ,000 C from the cracking furnacecontaining reaction products, diluent such steam and cracked coke isdirectly injected into molten metal in the quenching tower 7 andquenched to 300-500 C in order to avoid secondary reaction ofhydrocarbons as much as possible. The quenching tower 7 is filled withmolten metal supplied through an inlet 11, in which the quencher tube 8is placed. The gaseous reaction products are vigorously mixed with themolten metal and thereby quenched. The gaseous reaction products and thediluent ascend and are discharged through an outlet 10. On the otherhand, cracked coke, etc., produced in the reaction tube 3 and thequenching tower 7 float on the surface level of the molten metal in thequenching tower 7 owing to difference in specific gravity, whereby theyare separated from the molten metal and taken out through a side outlet9. Thus, in the quenching tower 7, the molten metal as circulatingliquid, reaction products and diluent from the reaction tube .arequenched and also the gaseous reaction products containing the diluentand cracked coke can be separated from the molten metal and taken outfrom the system separately. The quenched molten metal is sent from thebottom of the quenching tower into the cracking furnace 5 again,preheated and circulated into the reaction tube for thermal cracking ofhydrocarbons. The circulation of the molten metal as circulating liquidis facilitated by keeping the surface of the molten metal in thequenching tower at a level higher than the reaction tube 3 and byspraying liquid or gaseous hydrocarbon feed stock or a diluent such assteam through the feed stock supplying nozzles at a high speed. Themolten metal thus circulates in the cracking furnace and the quenchingtower, and so conveying equipment as pump is unnecessary and loss ofmolten metal is quite small.

As described above in detail, according to the present invention,hydrocarbons can be thermally cracked, the reaction products can bequenched and cracked coke can be removed by circulating molten metal ascirculating fluid in the system. In other words, the present inventionhas a merit of carrying out all of quenching, transfer and separation ofcracked coke at the same time in a simple quenching tower withoutnecessitating respective devices. In addition, reaction temperature,residence time .or the like can be selected optionally by varying amountof feed stock, length, diameter and number of the reactor tubes,consumption of fuel oil and kind and circulating amount of moltenmetals.

We claim:

1. A process for the thermal cracking of hydrocarbons which comprisesflowing molten metal at a temperature of at least about 700 C. togetherwith a hydrocarbon feed stock through an elongated metal reaction tubewhereby said feed stock is vaporized and thermally cracked, dischargingthe effluent molten metal and vaporized hydrocarbon reaction productsdirectly from said reaction tube into a quenching zone below the surfaceof a bath of molten metal to cool said reaction products to atemperature in the range from about 300 to about 500 C., and withdrawingthe vaporized hydrocarbon reaction products from said quenching zone,whereby any coke formed in the cracking operation and any othercarbonaceous material present in other than vapor form accumulates inthe molten metal bath and floats to the surface thereof.

2. A process according to claim 1 wherein steam is introduced with thehydrocarbon feed stock.

3. A process according to claim 1 wherein said reaction tube isexternally heated.

4. A process according to claim 1 wherein molten metal is withdrawn fromsaid quenching zone, heated to a temperature of at least 700 C. andrecycled to said reaction tube.

5. A process according to claim 1 wherein molten metal is withdrawn fromsaid quenching zone and recycled to said reaction tube through aconduit, and wherein said reaction tube and said conduit containingrecycled molten metal are heated externally.

6. A process according to claim 5 wherein steam is introduced with thehydrocarbon feed stock.

UNITED STATES PATENT OFFICE (IERTI FICATE. OF CORRECTIUN Patent N6.3,696,166 1 j Dat d October 3, 1972 In vent r( j v Ozawa 6t 31 It iscertified that error appears in the above-identified patent and thatsaid- Letters Patent are hereby corrected as shown below:

On the cover sheet" insert [73] Assignee: Mitsui Shipbuilding andEngineering Company, Ltd. Tokyo, Japan, a jcorporation of Japan Column2, line 23, "such steam" should read suchaseteam Signed and sealedthis10th day Of April 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR; ROBERT GOTTSCHALK Attesting Officer 6 g i v vCommissioner of Patents FORM Po-1 050 (10-69) USCOMM-DC 60376-1 69 ru.sv GQVERNMENT PRINTING OFFICE 1 (959 o-ase-aaa.

2. A process according to claim 1 wherein steam is introduced with thehydrocarbon feed stock.
 3. A process according to claim 1 wherein saidreaction tube is externally heated.
 4. A process according to claim 1wherein molten metal is withdrawn from said quenching zone, heated to atemperature of at least 700* C. and recycled to said reaction tube.
 5. Aprocess according to claim 1 wherein molten metal is withdrawn from saidquenching zone and recycled to said reaction tube through a conduit, andwherein said reaction tube and said conduit containing recycled moltenmetal are heated externally.
 6. A process according to claim 5 whereinsteam is introduced with the hydrocarbon feed stock.